The invention relates to a method and a device for the centrifugal skimming of whey in which raw whey is fed to a feeding device of a skimming separator and is broken down into a skimmed whey phase and into a whey cream phase. Discharge devices then expel this from the skimming separator.
The concentration of the whey cream is adjusted by a control valve provided in the whey cream discharge line. The raw whey is the liquid resulting from the production of cheese after the separation of the case in and of the fat when the milk curdles.
The fat content of the raw whey to be skimmed, as a rule, is relatively low: approximately 0.1 to 0.2 percent. In contrast, the whey cream flowing out of the skimming separator has approximately 30% fat content. This results in a cream quantity which, in the least favorable case, corresponds to only {fraction (1/300)} of the fed raw whey. In the case of such a low cream quantity, only a low flow rate is achieved in the skimming separator. At low flow rates, a minimal disturbance, such as a burst of air, may interrupt the cream flow and thus impair the skimming intensity of the skimming separator. In addition, the cream can form oil at this low flow rate.
Another disturbance factor is the very different fat content in the raw whey which can change from one cheese producer to another cheese producer abruptly within the above-mentioned values of from 0.1 to 0.4%. This means that the quantities flowing from the whey cream discharge line can change by the factor 4. Because of the relatively small whey quantity and the potential for abrupt change of this quantity, automatic regulation of the concentration has not been used successfully.
It is an object of the invention to provide a process for the centrifugal skimming of whey which not only provides a better fat quality of the cream but also permits automatic regulation of the cream concentration. In addition, a device is to be designed for implementing this method.
According to the invention, a quantity of whey cream is returned via a recirculation line into the feed line of the skimming separator; it is found that a quantity of 0.5 to 2 percent of the volumetric flow of the raw whey fed to the skimming separator is best.
In a preferred embodiment of the method according to the invention, in the recirculation line a constant volumetric flow with constant pressure conditions is adjusted and density measurements are transmitted to an evaluation device which regulates the control valve in the whey cream discharge line.
The device for implementing the method according to the invention has a skimming separator having a feed line for raw whey and discharge lines for skimmed whey and whey cream. From the whey cream discharge line, a recirculation line branches off, allowing a portion of the whey cream into the feed line for the raw whey. A fluidimeter and a density transmitter are placed in the recirculation line, and connected with an evaluation device which can selectively operate the control valve in the whey cream discharge line.
The method according to the invention and the device required for implementing the method are described in detail by means of FIGS. 1 and 2.